Transverse flux induction heating device

ABSTRACT

The transverse flux induction heating device is allows an alternating magnetic field to intersect the sheet face of a conductive sheet which is conveyed in one direction, thereby inductively heating the conductive sheet. The transverse flux induction heating device includes a heating coil disposed such that a coil face faces the sheet face of the conductive sheet; a core around which the heating coil is coiled; a shielding plate formed of a conductor and disposed between the core and a side end portion in the direction perpendicular to a conveyance direction of the conductive sheet; and a non-conductive  10  soft magnetic material which is attached to the shielding plate, wherein the shielding plate is interposed between the core and the non-conductive soft magnetic material.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Divisional of copending application Ser. No.13/577,967 filed on Aug. 9, 2012, which is a national stage applicationof International Application No. PCT/JP2011/053526, filed Feb. 18, 2011,which claims priority to Japanese Patent Application No. 2010-35198,filed on Feb. 19, 2010, the contents of which are incorporated herein byreference.

FIELD OF THE INVENTION

The present invention relates to a transverse flux induction heatingdevice. In particular, the transverse flux induction heating device issuitably used to inductively heat a conductive sheet by making analternating magnetic field approximately perpendicularly intersect theconductive sheet.

DESCRIPTION OF RELATED ART

In the past, heating a conductive sheet such as a steel sheet, using aninduction heating device has been performed. The induction heatingdevice generates Joule heat based on an eddy current which is induced inthe conductive sheet by an alternating magnetic field (analternating-current magnetic field) generated from a coil, in theconductive sheet, and heats the conductive sheet by the Joule heat. Atransverse flux induction heating device is one type of such aninduction heating device. The transverse flux induction heating deviceheats a conductive sheet of a heating target by making an alternatingmagnetic field approximately perpendicularly intersect the conductivesheet.

In the case of using such a transverse flux induction heating device,unlike the case of using a solenoid-type induction heating device, thereis a problem in that both ends (both side ends) in the width directionof the conductive sheet of the heating target become overheated.

The techniques described in Patent Citation 1 and Patent Citation 2 aretechniques related to such a problem.

In the technique described in Patent Citation 1, a movable plainshielding plate made of a non-magnetic metal is provided between a coiland each of both side ends of a conductive sheet of a heating target.

Further, in the technique described in Patent Citation 2, a rhombic coiland an oval coil which have different heating patterns are disposedalong the conveyance direction of a conductive sheet of a heatingtarget, thereby heating the conductive sheet in a desired heatingpattern with respect to the width direction of the conductive sheet.

PATENT CITATION

[Patent Citation 1] Japanese Unexamined Patent Application, FirstPublication No. S62-35490

[Patent Citation 2] Japanese Unexamined Patent Application, FirstPublication No. 2003-133037

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

However, by only providing a simple plate-shaped shielding plate betweenthe coil and each of both side ends of the conductive sheet of theheating target, as in the technique described in Patent Citation 1,since the eddy current spreads in an area slightly to the inside of bothside ends of the conductive sheet, eddy current density is small, andsince eddy currents flowing in both side ends of the conductive sheetcannot flow out of the conductive sheet, eddy current density becomeslarge at both side ends. Therefore, it is difficult to lower thetemperatures of both side ends of the conductive sheet and thesmoothness of the temperature distribution in the width direction of theconductive sheet is also significantly lowered (in particular, the slopeof the temperature distribution at each of both side ends of theconductive sheet becomes large).

Further, in the technique described in Patent Citation 2, it is possibleto suppress lowering of the smoothness of the temperature distributionin the width direction of a specific conductive sheet. However, if thesheet width of the conductive sheet is changed, the coil has to be resetdepending on the sheet width. Therefore, a mechanism for moving the coilis required and it is difficult to easily and quickly respond to achange in sheet width.

In addition, in the techniques described in Patent Citation 1 and PatentCitation 2, if the conductive sheet moves in a meandering manner, thesmoothness of the temperature distribution in the width direction of theconductive sheet is lowered.

The present invention has been made in view of such problems and has anobject of providing a transverse flux induction heating device whichallows unevenness of a temperature distribution in the width directionof a conductive sheet of a heating target to be reduced and allowsvariations in temperature distribution in the width direction of theconductive sheet of the heating target due to meandering of theconductive sheet to be reduced.

Methods for Solving the Problem

(1) A transverse flux induction heating device according to an aspect ofthe present invention allows an alternating magnetic field to intersectthe sheet face of a conductive sheet which is conveyed in one direction,thereby inductively heating the conductive sheet. The transverse fluxinduction heating device includes: a heating coil disposed such that acoil face faces the sheet face of the conductive sheet; a core aroundwhich the heating coil is coiled; a shielding plate formed of aconductor and disposed between the core and a side end portion in adirection perpendicular to the conveyance direction of the conductivesheet; and a non-conductive soft magnetic material which is attached tothe shielding plate, wherein the shielding plate is interposed betweenthe core and the non-conductive soft magnetic material.

(2) The transverse flux induction heating device according to the above(1) may further include a heat-resistant plate which is attached to thenon-conductive soft magnetic material, wherein the heat-resistant plateis disposed closer to the conductive sheet than the non-conductive softmagnetic material.

(3) In the transverse flux induction heating device according to theabove (1), the shielding plate may have a cross section parallel to thecoil face, and the cross section may include the non-conductive softmagnetic material.

(4) In the transverse flux induction heating device according to theabove (1), a depressed portion which faces the side end portion in thedirection perpendicular to the conveyance direction of the conductivesheet may be formed in the surface facing the conductive sheet of theshielding plate and the non-conductive soft magnetic material may behoused in the depressed portion.

(5) In the transverse flux induction heating device according to theabove (4), a portion which is tapered off toward a side close to acentral portion in a direction perpendicular to the conveyance directionof the conductive sheet from a side away from the central portion in thedirection perpendicular to the conveyance direction of the conductivesheet may be included in the depressed portion.

(6) In the transverse flux induction heating device according to theabove (4), a first portion which is tapered off toward the downstreamside from the upstream side in the conveyance direction of theconductive sheet and a second portion which is tapered off toward theupstream side from the downstream side in the conveyance direction ofthe conductive sheet may be included in the depressed portion, and thefirst portion and the second portion may face each other in theconveyance direction of the conductive sheet.

(7) In the transverse flux induction heating device according to theabove (6), the first portion may be rounded toward the downstream sideand the second portion may be rounded toward the upstream side.

Effects of the Invention

According to the present invention, the non-conductive soft magneticmaterial is mounted on the shielding plate which is disposed between thecore around which the coil is coiled and an end portion in the widthdirection of the conductive sheet. Through the non-conductive softmagnetic material, the magnitude of an eddy current in the shieldingplate, which flows in the vicinity of the non-conductive soft magneticmaterial, can be made large. Therefore, unevenness of the temperaturedistribution in the width direction of the conductive sheet of a heatingtarget can be reduced and variations in the temperature distribution inthe width direction of the conductive sheet of the heating target due tomeandering of the conductive sheet can be reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view showing one example of the schematic configurationof a continuous annealing line for a steel sheet according to anembodiment of the present invention.

FIG. 2A is a vertical cross-sectional view showing one example of theconfiguration of an induction heating device according to thisembodiment.

FIG. 2B is a vertical cross-sectional view showing one example of theconfiguration of the induction heating device according to thisembodiment.

FIG. 2C is a fragmentary perspective view showing one example of theconfiguration of the induction heating device according to thisembodiment.

FIG. 3 is a diagram showing one example of the configurations of anupper side heating coil and a lower side heating coil according to thisembodiment.

FIG. 4A is a top view showing one example of the configuration of ashielding plate according to this embodiment.

FIG. 4B is a vertical cross-sectional view showing one example of theconfiguration of the shielding plate according to this embodiment.

FIG. 4C is a vertical cross-sectional view showing one example of theconfiguration of the shielding plate according to this embodiment.

FIG. 4D is a fragmentary view when an area including a shielding plate31 d according to this embodiment is viewed from directly above a steelstrip 10.

FIG. 4E is a transverse cross-sectional view showing one example of theconfiguration of the shielding plate according to this embodiment.

FIG. 5 is a diagram showing one example of the relationship between theamount of insertion of the shielding plate and a width temperaturedeviation ratio in an example using this embodiment.

FIG. 6A is a top view showing one example of the configuration of ashielding plate according to the first modified example of thisembodiment.

FIG. 6B is a top view showing one example of the configuration of ashielding plate according to the second modified example of thisembodiment.

FIG. 6C is a vertical cross-sectional view showing one example of theconfiguration of a shielding plate according to the third modifiedexample of this embodiment.

FIG. 7A is a vertical cross-sectional view showing one example of theconfiguration of a shielding plate according to the fourth modifiedexample of this embodiment.

FIG. 7B is a vertical cross-sectional view showing one example of theconfiguration of a shielding plate according to the fifth modifiedexample of this embodiment.

FIG. 7C is a vertical cross-sectional view showing one example of theconfiguration of a shielding plate according to the sixth modifiedexample of this embodiment.

FIG. 8A is a perspective view showing one example of the configurationof a shielding plate according to the seventh modified example of thisembodiment.

FIG. 8B is a perspective view showing one example of the configurationof a shielding plate according to the eighth modified example of thisembodiment.

FIG. 8C is a perspective view showing one example of the configurationof a shielding plate according to the ninth modified example of thisembodiment.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, an embodiment of the present invention will be describedreferring to the drawings. In this embodiment, a case where a transverseflux induction heating device is applied to a continuous annealing linefor a steel sheet is described as an example. In addition, in thefollowing description, the “transverse flux induction heating device” isreferred to as an “induction heating device” for brevity, as necessary.

[Configuration of Continuous Annealing Line]

FIG. 1 is a side view showing one example of the schematic configurationof a continuous annealing line for a steel sheet. In addition, in eachdrawing, for convenience of explanation, only the necessaryconfiguration is simplified and shown.

In FIG. 1, a continuous annealing line 1 includes a first container 11,a second container 12, a third container 13, a first sealing rollerassembly 14, a conveyance unit 15, a second sealing roller assembly 16,a gas supply unit 17, an alternating-current power supply unit 18,rollers 19 a to 19 u (19), and an induction heating device 20.

The first sealing roller assembly 14 transports a steel strip (astrip-shaped sheet, a conductive sheet) 10 into the first container 11while shielding the first container 11 from the external air. The steelstrip 10 conveyed into the first container 11 by the first sealingroller assembly 14 is conveyed into the second container 12 by therollers 19 a and 19 b in the first container 11. The steel strip 10conveyed into the second container 12 is conveyed into the firstcontainer 11 again by the rollers 19 g and 19 h while being heated bythe induction heating device 20 disposed above and below the horizontalportion of the second container 12 (the steel strip 10 which isconveyed). Here, the induction heating device 20 is electricallyconnected to the alternating-current power supply unit 18 and receivesalternating-current power from the alternating-current power supply unit18, thereby generating an alternating magnetic field which intersectsapproximately perpendicularly to the sheet face of the steel strip 10,and inductively heating the steel strip 10. In addition, the details ofthe configuration of the induction heating device 20 will be describedlater. Further, in the following explanation, “electrical connection” isreferred to as “connection” for brevity, as necessary.

The steel strip 10 returned into the first container 11 is conveyed tothe conveyance unit 15 by way of a soaking and slow cooling stage by therollers 19 c to 19 f. The steel strip 10 conveyed to the conveyance unit15 is conveyed into the third container 13 by the rollers 19 i and 19 j.The steel strip 10 conveyed into the third container 13 is conveyedwhile being moving in a vertically up and down manner by the rollers 19k to 19 u and rapidly cooled in the third container 13.

The second sealing roller assembly 16 sends the steel strip 10 rapidlycooled in this way to a post-process while blocking the third container13 from external air.

Into “the first container 11, the second container 12, the thirdcontainer 13, and the conveyance unit 15” which become a “transportpathway of the steel strip 10” as described above, non-oxidizing gas issupplied by the gas supply unit 17. Then, by “the first sealing rollerassembly 14 and the second sealing roller assembly 16” which block theinside (the inside of the continuous annealing line 1) from the outside(external air), a non-oxidizing gaseous atmosphere is maintained in thefirst container 11, the second container 12, the third container 13, andthe conveyance unit 15.

[Configuration of Induction Heating Device]

FIGS. 2A to 2C are diagrams showing one example of the configuration ofthe induction heating device.

Specifically, FIG. 2A is a diagram showing one example of the inductionheating device 20 in this embodiment, as viewed from a side of thecontinuous annealing line, and is a vertical cross-sectional view cut(in the up-and-down direction in FIG. 1) along the longitudinaldirection of the steel strip 10. In FIG. 2A, the steel strip 10 isconveyed in the left direction (refer to an arrow pointing from theright to the left in FIG. 2A). Further, FIG. 2B is a verticalcross-sectional view showing one example of the induction heating device20 in this embodiment, as viewed in a direction of A-A′ in FIG. 1 (thatis, a diagram as viewed from the downstream in a sheet conveyancedirection). In FIG. 2B, the steel strip 10 is conveyed in a directionfrom the back of the drawing to the front. Further, FIG. 2C is afragmentary perspective view partially showing one example of theinduction heating device 20 in this embodiment. In FIG. 2C, a lowerright area shown in FIG. 2B is looked down from above the steel strip10.

In FIGS. 2A to 2C, the induction heating device 20 includes an upperside inductor 21 and a lower side inductor 22.

The upper side inductor 21 includes a core 23, an upper side heatingcoil (a heating coil) 24, and shielding plates 31 a and 31 c.

The upper side heating coil 24 is a conductor coiled around the core 23through a slot of the core 23 (here, a depressed portion of the core 23)and is a coil (a so-called single turn) in which the number of turns is“1”. Further, as shown in FIG. 2A, the upper side heating coil 24 has aportion, the vertical cross-sectional shape of which is a hollowrectangle. A water-cooling pipe is connected to the end face of a hollowportion of the hollow rectangle. Cooling water which is supplied fromthe water-cooling pipe flows in the hollow portion (the inside of theupper side heating coil 24) of the hollow rectangle, so that the upperside inductor 21 is cooled. Further, the shielding plates 31 a and 31 care mounted on the bottom surface (the slot side) of the core 23.

In addition, in FIG. 2A, a length l₁ in the upper side inductor 21 is 45[mm], a length l₂ is 180 [mm], a length l₃ is 80 [mm], a length l₄ is180 [mm], a length l₅ is 45 [mm], a length l₆ is 45 [mm], and a lengthl₇ is 45 [mm]. Further, a width W of the steel strip 10 is 900 [mm] anda thickness d_(s) is 0.3 [mm]. However, these dimensions are not limitedto the values described above.

The lower side inductor 22 includes a core 27, a lower side heating coil(a heating coil) 28, and shielding plates 31 b and 31 d, similarly tothe upper side inductor 21.

The lower side heating coil 28 is also a conductor coiled around thecore 27 through a slot of the core 27 and is a coil (a so-called singleturn) in which the number of turns is “1”, similarly to the upper sideheating coil 24. Further, the lower side heating coil 28 has a portion,the vertical cross-sectional shape of which is a hollow rectangle,similarly to the upper side heating coil 24. A water-cooling pipe isconnected to the end face of a hollow portion of the hollow rectangleand can flow cooling water into the hollow portion of the hollowrectangle.

Further, a coil face (a face in which a loop is formed; a face in whicha line of magnetic force penetrates) of the upper side heating coil 24of the upper side inductor 21 and a coil face of the lower side heatingcoil 28 of the lower side inductor 22 face each other with the steelstrip 10 interposed therebetween. In addition, the plate faces of theshielding plates 31 a to 31 d (31) face side end portions (edges) in thesheet width direction of the steel strip 10. In order to satisfy such apositional relationship, the upper side inductor 21 is provided furtheron the upper side (in the vicinity of the upper surface of thehorizontal portion of the second container 12) than the steel strip 10and the lower side inductor 22 is provided further on the lower side (inthe vicinity of the lower surface of the horizontal portion of thesecond container 12) than the steel strip 10.

As described above, the upper side inductor 21 and the lower sideinductor 22 are different in the position to be disposed, but have thesame configuration.

Further, in this embodiment, the shielding plates 31 a to 31 d can beindividually moved in the width direction (a direction of adouble-headed arrow shown in FIG. 2B) of the steel strip 10 based on anoperation of a driving device (not shown).

Further, in this embodiment, a distance d between the upper side heatingcoil 24 and the lower side heating coil 28, the heating coil widths 12and 14 in the upper side heating coil 24, and the heating coil widths 12and 14 in the lower side heating coil 28 are the same. Further, aposition where an “overlap length R in the width direction of the steelstrip 10” between each of both side end portions of the steel strip 10and each of the shielding plates 31 a to 31 d is 90 [mm] is defined asthe reference position.

Here, the heating coil width is the length in the width direction of theupper side heating coil 24 (the lower side heating coil 28) that is inthe slot. In the example shown in FIG. 2A, the heating coil width isequal to the length in the width direction of each of the copper pipes41 a to 41 d shown in FIG. 3, which will be described later, and isapproximately the same length as the width of the slot of each of thecores 23 and 27.

In addition, in the following explanation, each of the heating coilwidth of the upper side heating coil 24 and the heating coil width ofthe lower side heating coil 28 is simply referred to as a heating coilwidth, as necessary, and the distance between the upper side heatingcoil 24 and the lower side heating coil 28 is referred to as a gap, asnecessary.

[Configuration of Heating Coil]

FIG. 3 is a diagram showing one example of the configurations of theupper side heating coil 24 and the lower side heating coil 28. Inaddition, an arrow shown in FIG. 3 represents one example of a directionin which an electric current flows at a certain time.

As shown in FIG. 3, the upper side heating coil 24 has the copper pipes41 a and 41 b, and a copper bus bar (a connection plate) 42 b which isconnected to the base end sides of the copper pipes 41 a and 41 b.Further, the lower side heating coil 28 has the copper pipes 41 c and 41d, and a copper bus bar 42 f which is connected to the base end sides ofthe copper pipes 41 c and 41 d.

One end (the front end side of the copper pipe 41 a) of the upper sideheating coil 24 and an output terminal on one side of thealternating-current power supply unit 18 are mutually connected througha copper bus bar 42 a. On the other hand, the other end (the front endside of the copper pipe 41 b) of the upper side heating coil 24 and oneend (the front end side of the copper pipe 41 c) of the lower sideheating coil 28 are mutually connected through copper bus bars 42 c to42 e. Further, the other end (the front end side of the copper pipe 41d) of the lower side heating coil 28 is mutually connected to an outputterminal on the other side of the alternating-current power supply unit18 through copper bus bars 42 i, 42 h, and 42 g.

As described above, the upper side heating coil 24 and the lower sideheating coil 28 are connected in series with respect to thealternating-current power supply unit 18 by the combination of thecopper pipes 41 a to 41 d (41) and the copper bus bars 42 a to 42 i (42)and form coils each of which the number of turns is “1”. In FIG. 3, alarge magnetic flux is generated toward the bottom from the top of acentral portion surrounded by the copper pipes 41 and the copper busbars 42, and the magnetic flux passes through the steel strip 10,whereby Joule heat is generated in the steel strip 10, so that the steelstrip 10 is heated.

In addition, here, in order to clearly illustrate the configurations ofthe upper side heating coil 24 and the lower side heating coil 28, asshown in FIG. 3, the copper pipes 41 a to 41 d and the copper bus bars42 a to 42 g are connected to each other. However, when the upper sideheating coil 24 and the lower side heating coil 28 are coiled around thecores 23 and 27, there is a need to pass (attach) the copper pipes 41 ato 41 d through the slots of the cores 23 and 27. Therefore, in fact,the copper bus bars 42 are attached to the copper pipes 41 a to 41 d toavoid portions where the copper pipes 41 are installed to the cores 23and 27.

<Configuration of Shielding Plate>

FIGS. 4A to 4E are diagrams showing one example of the configuration ofthe shielding plate 31.

Specifically, FIG. 4A is a top view of the shielding plate 31 whenviewed from directly above (the steel strip 10 side). Further, FIG. 4Bis a vertical cross-sectional view as viewed from the direction of A-A′in FIG. 4A. FIG. 4C is a vertical cross-sectional view as viewed fromthe direction of B-B′ in FIG. 4A. FIG. 4D is a view when an areaincluding the shielding plate 31 d shown in FIG. 2C is viewed fromdirectly above the steel strip 10. FIG. 4E is a transversecross-sectional view as viewed from the direction of C-C′ in FIG. 4B. Inaddition, in FIG. 4D, only a portion which is required to explain thepositional relationship between the steel strip 10 and the shieldingplate 31 d is shown. Further, in FIG. 4D, eddy currents I_(e), I_(h1),and I_(h2) which flow in the shielding plate 31 d are conceptuallyshown. In addition, the steel strip 10 is conveyed in the direction ofan arrow shown in the right end in FIGS. 4A and 4D.

In addition, a conveyance direction of the steel strip 10 approximatelycorresponds to the depth direction of the shielding plate 31, and adirection (the width direction of the steel strip 10) perpendicular tothe conveyance direction of the steel strip 10 on the sheet faceapproximately corresponds to the width direction of the shielding plate.Further, the plate thickness (the thickness) direction of the shieldingplate 31 approximately corresponds to a direction (the sheet thicknessdirection of the steel strip 10) perpendicular to the coil face of theheating coil (for example, the upper side heating coil 24).

In FIGS. 4A to 4C, the shielding plate 31 is made of copper and hasdepressed portions 51 a and 51 b (51) having the same size and shape.The depressed portions 51 a and 51 b are disposed to have a distancetherebetween in the conveyance direction of the steel strip 10.

As shown in FIG. 4A, the shape (the opening shape) in the plate facedirection (the plate thickness direction of the shielding plate 31) ofeach of the depressed portions 51 a and 51 b is a rhombus in which eachof the corner portions 54 a to 54 h (54) is rounded.

In FIG. 4A, a distance P between a corner portion which is an endportion of the depressed portion 51 a and is on the upstream side in theconveyance direction of the steel strip 10 and a corner portion which isan end portion of the depressed portion 51 b and is on the downstreamside in the conveyance direction of the steel strip 10 is 150 [mm].Further, a distance Q between a corner portion which is an end portionof the depressed portion 51 a and is located in the center in theconveyance direction of the steel strip 10 and a corner portion which isan end portion of the depressed portion 51 b and is located in thecenter in the conveyance direction of the steel strip 10 is 310 [mm].

As shown in FIG. 4D, in this embodiment, the shielding plate 31 is movedin the width direction of the steel strip 10 such that a side end 10 aof the steel strip 10 and the depressed portions 51 a and 51 b overlapeach other when viewed from the up-and-down direction. As a specificexample thereof, the side end 10 a of the steel strip 10 and the longestportions on the plate face of the depressed portions 51 a and 51 b(diagonal line portions of the rounded rhombuses parallel to theconveyance direction of the steel strip 10) overlap each other whenviewed from the up-and-down direction (a direction perpendicular to thesheet face of the steel strip 10).

By disposing the shielding plate 31 so as to be in such a positionalrelationship, a main magnetic flux, which is generated by operating theinduction heating device 20, and thereby flowing an alternating currentin the upper side heating coil 24 and the lower side heating coil 28,can be shielded by the shielding plate 31. However, eddy currents aregenerated in both side end portions of the steel strip 10 by the mainmagnetic flux, and the eddy current touches the side end of the steelstrip, so that a current density in the side end becomes high and adifference in temperature occurs between the side end and the vicinitythereof. Therefore, the inventors have found from the results ofextensive studies that the difference in temperature can be reduced byhousing non-conductive soft magnetic plates 52 a and 52 b (52), each ofwhich is composed of a soft magnetic ferrite (for example, a Mn—Zn-basedferrite or a Ni—Zn-based ferrite) or the like, into the above-mentioneddepressed portions 51 a and 51 b. Here, the non-conductive soft magneticplates 52 a and 52 b can be fixed to the depressed portions 51 a and 51b of the shielding plate 31 using, for example, an adhesive.

That is, as shown in FIG. 4D, if a portion of the eddy current I_(e)which flows so as to go around the end portion of the shielding plate 31is branched so that the eddy currents I_(h1) and I_(h2) flow along theedges of the depressed portions 51 a and 51 b, an eddy current of thesteel strip 10 which is generated by magnetic fields that are created bythe eddy currents I_(h1) and I_(h2) cancels out and weakens an eddycurrent (an eddy current due to the main magnetic flux) which flows inthe side end portion of the steel strip 10. As a result, the effect ofpushing the eddy current which flows in the side end portion of thesteel strip 10 into the inside in the width direction of the steel strip10 can be produced, so that homogenization of eddy current density inthe vicinity of the side end 10 a of the steel strip 10 progresses and adifference in temperature between the side end portion (ahigh-temperature portion) of the steel strip 10 and a portion (alow-temperature portion) further inside than the side end portion isreduced.

Therefore, large eddy currents I_(h1) and I_(h2) need to flow along theedges of the depressed portions formed in the shielding plate. Theinventors have obtained knowledge that in the shielding plate with onlya depressed portion simply formed therein, there is a possibility thatthe effect of reducing the above-mentioned difference in temperaturecannot be reliably obtained. This is considered to be because an eddycurrent continuously flows through the bottom surface of the depressedportion. Therefore, the inventors have found that by housing thenon-conductive soft magnetic plates 52 a and 52 b in the depressedportions 51 a and 51 b of the shielding plate 31, as described above, itis possible to strengthen a magnetic field which is generated by theeddy current flowing in the shielding plate 31 due to the main magneticflux. By the strengthening of the magnetic field, it is possible to makethe magnitude of the eddy current which is branched from a pathway goingaround the end portion of the shielding plate 31 larger. As a result, itis possible to make the magnitudes of the eddy currents I_(h1) andI_(h2) which flow along the edges of the depressed portions 51 a and 51b larger (than where are the non-conductive soft magnetic plates 52 aand 52 b not being housed).

For the reason as described above, in this embodiment, thenon-conductive soft magnetic plates (non-conductive soft magneticmaterials) 52 a and 52 b are housed in the depressed portions 51 a and51 b formed in the shielding plate 31. In the case of using conductivematerials in place of the non-conductive soft magnetic plates 52 a and52 b, since the shielding plate itself is conductive, the conductivematerial and the shielding plate act as an integrated conductive member,so that it is not possible to strongly limit the distribution of theeddy current to the edges of the depressed portions 51 a and 51 b.

In addition, in this embodiment, heat-resistant plates 53 a and 53 b(53) which protect the non-conductive soft magnetic plates 52 a and 52 bfrom heat from the outside are disposed on the top (the steel strip 10side) of the non-conductive soft magnetic plates 52 a and 52 b in thedepressed portions 51 a and 51 b and fixed thereto by, for example, anadhesive.

In FIGS. 4A to 4C, a thickness D of the shielding plate 31 is 25 [mm]and a depth D_(m) of each of the depressed portions 51 a and 51 b is 15[mm]. Each of the non-conductive soft magnetic plates 52 a and 52 b hasa shape corresponding with the shape (the shape of a cross-sectionperpendicular to the thickness direction of the shielding plate 31) inthe plate face direction of the bottom portion of each of the depressedportions 51 a and 51 b, and a thickness D_(F) thereof is 5 [mm].However, these dimensions are not limited to the values described above.The inventors have confirmed that in a frequency range (5 [kHz] to 10[kHz]) which is used in the induction heating device 20, if thethickness D_(F) is equal to or more than 1 [mm] (and is equal to or lessthan the depth of each of the depressed portions 51 a and 51 b), in acase where the non-conductive soft magnetic plates 52 a and 52 b arehoused and a case where the non-conductive soft magnetic plates 52 a and52 b are not housed, a sufficient difference occurs in the effect ofreducing the above-mentioned difference in temperature. Further, each ofthe heat-resistant plates 53 a and 53 b has a shape corresponding withthe shape (the shape of a cross-section perpendicular to the thicknessdirection of the shielding plate 31) in the plate face direction of thebottom portion of each of the depressed portions 51 a and 51 b of theshielding plate 31, and a thickness D_(D) thereof is 10 [mm].

As described above, by housing the non-conductive soft magnetic plates52 a and 52 b in the depressed portions 51 a and 51 b, a magnetic fieldwhich is generated by an eddy current flowing in the shielding plate 31due to the main magnetic flux is strengthened. By the strengthening ofthe magnetic field, the magnitudes of the eddy currents I_(h1) andI_(h2) flowing along the edges of the depressed portions 51 a and 51 balso become larger. Therefore, magnetic fields which are generated bythese large eddy currents also become large, so that a larger eddycurrent which cancels out the eddy current flowing in the side endportion of the steel strip 10 can be produced in the vicinity of theside end portion. As a result, the effect of sufficiently pushing theeddy current of the side end portion of the steel strip 10 which isproduced by the main magnetic flux into the inside in the widthdirection of the steel strip 10 is produced.

Further, as described above, in this embodiment, the corner portions 54a to 54 h of the depressed portions 51 a and 51 b are rounded. However,it is acceptable if at least the corner portions 54 a and 54 e which arethe “corner portions on the downstream side in the conveyance directionof the steel strip 10” of the depressed portions 51 a and 51 b arerounded so as to protrude in the downstream side direction and thecorner portions 54 b and 54 f which are the “corner portions on theupstream side in the conveyance direction of the steel strip 10” of thedepressed portions 51 a and 51 b are rounded so as to protrude in theupstream side direction. If doing so, even if the steel strip 10 movesin a meandering manner, it is possible to reduce the amount of change inthe “overlap length in the conveyance direction of the steel strip 10”between the side end 10 a of the steel strip and each of the depressedportions 51 a and 51 b″ when viewed from the up-and-down direction, andit is also possible to reduce the amount of change in the effect ofpushing the eddy current of the side end portion of the steel strip 10further toward the inside than the side end portion. Further, asdescribed above, since the eddy currents I_(h1) and I_(h2) flowing alongthe edges of the depressed portions 51 a and 51 b become large due tothe non-conductive soft magnetic plates 52 a and 52 b, even if the steelstrip 10 moves in a meandering manner, the magnitudes of the eddycurrents I_(h1) and I_(h2) and the effect of pushing the eddy currentflowing in the side end portion of the steel strip 10 further toward theinside than the side end portion can be maintained to some extent.Therefore, even if the steel strip 10 moves in a meandering manner, achange in temperature distribution in the width direction of the steelstrip 10 can be reduced.

EXAMPLE

FIG. 5 is a diagram showing one example of the relationship between theamount of insertion of the shielding plate and a width temperaturedeviation ratio.

The amount of insertion of the shielding plate corresponds to the“overlap length R in the width direction of the steel strip 10” betweeneach of both side end portions of the steel strip 10 and each shieldingplate (refer to FIG. 2B). Further, the width temperature deviation ratiois a value (=sheet width central portion temperature/sheet end portiontemperature) obtained by dividing the temperature of the central portionin a temperature distribution in the width direction of the steel strip10 (the sheet width central portion temperature) by the temperature ofthe end portion (the sheet end portion temperature).

In FIG. 5, in a graph A1, a plain shielding plate in which no depressedportion is formed is used. In a graph A2, a shielding plate having thedepressed portions in which the non-conductive soft magnetic plates arehoused, as in this embodiment, is used.

Here, the graphs shown in FIG. 5 are based on the results of experimentsperformed under the following conditions.

Heating coil width: 1300 [mm]

Material of core: ferrite

Material to be heated: stainless steel sheet (width of 900 [mm], andthickness of 0.3 [mm])

Gap between coils: 180 [mm]

Sheet conveyance speed: 50 [mpm (m/min.)]

Heating temperature: 400 to 730 [° C.] (the temperature increase of thecenter is set to be 330 [° C.])

Power-supply frequency: 8.5 [kHz]

Current: 3650 [AT]

Material of shielding plate: copper

External dimensions of shielding plate: width of 230 [mm], depth of 600[mm], and thickness of 25 [mm]

Shape of depressed portion of shielding plate: FIG. 4A (graph A2)

Material of non-conductive soft magnetic plate: Ni—Zn ferrite

Thickness of non-conductive soft magnetic plate: 5 [mm]

Standard of amount of insertion of shielding plate: 90 [mm]

In FIG. 5, it can be found that the smaller the width temperaturedeviation ratio (the closer to 1 the width temperature deviation ratio),the more uniform a temperature distribution in the width direction ofthe steel strip 10 can be. Further, it can be found that the smaller theslope of the graph, the greater the change in temperature distributionin the width direction of the steel strip 10 can be reduced even if thesteel strip 10 moves in a meandering manner.

In FIG. 5, it can be found that if the shielding plate having thedepressed portions in which the non-conductive soft magnetic plates arehoused is used, as in this embodiment, both the smoothing of atemperature distribution in the width direction of the steel strip 10and reduction of a change in the temperature distribution in the widthdirection of the steel strip 10 at the time of meandering of the steelstrip 10 can be realized.

SUMMARY

As described, in this embodiment, the shielding plate 31 is disposedbetween the side end portion of the steel strip 10 and each of the cores23 and 27 (the upper side heating coil 24 and the lower side heatingcoil 28). In the shielding plate 31, two depressed portions 51 a and 51b are formed so as to have a distance therebetween in the conveyancedirection of the steel strip 10. In addition, the non-conductive softmagnetic plates 52 a and 52 b are housed in the depressed portions 51 aand 51 b. Therefore, it is possible to strengthen a magnetic field whichis generated by the eddy current flowing in the shielding plate 31 d dueto the main magnetic flux and make the magnitudes of the eddy currentsI_(h1) and I_(h2) flowing along the edges of the depressed portions 51 aand 51 b larger. As a result, the smoothing of a temperaturedistribution in the width direction of the steel strip 10 can berealized. Further, by flowing the large eddy currents I_(h1) and I_(h2)along the edges of the depressed portions 51 a and 51 b in this manner,even if the steel strip 10 moves in a meandering manner, the effect inwhich the eddy currents I_(h1) and I_(h2) push the eddy current flowingin the side end portion of the steel strip 10 further toward the insidethan the side end portion can be maintained to some extent. Accordingly,even if the steel strip 10 moves in a meandering manner, a change intemperature distribution in the width direction of the steel strip 10can be reduced. In addition, even in a case where the steel strip 10moves in a meandering manner, a magnetic field which is generated by theeddy current flowing in the shielding plate 31 d pushes the side end ofthe steel strip 10 back to the center in the width direction of thesteel strip 10, so that meandering of the steel strip 10 can besuppressed.

Further, in this embodiment, the corner portions 54 a and 54 e which arethe “corner portions on the downstream side in the conveyance directionof the steel strip 10” of the depressed portions 51 a and 51 b arerounded so as to protrude in the downstream side direction and thecorner portions 54 b and 54 f which are the “corner portions on theupstream side in the conveyance direction of the steel strip 10” of thedepressed portions 51 a and 51 b are rounded so as to protrude in theupstream side direction. Therefore, even if the steel strip 10 moves ina meandering manner, it is possible to reduce the amount of change inthe “overlap length in the conveyance direction of the steel strip 10”between the side end 10 a of the steel strip and each of the depressedportions 51 a and 51 b″ when viewed from the up-and-down direction, sothat the amount of change in the push-in effect of the eddy currentflowing in the side end portion of the steel strip 10 can also bereduced. Accordingly, a change in temperature distribution in the widthdirection of the steel strip 10 when the steel strip 10 moves in ameandering manner can be even further reduced.

Further, in this embodiment, since the heat-resistant plates 53 a and 53b are disposed on the top (the steel strip 10 side) of thenon-conductive soft magnetic plates 52 a and 52 b, even if the inductionheating device is used under high temperature, degradation of thecharacteristics of the non-conductive soft magnetic plates 52 a and 52 bcan be prevented. However, in a case where the induction heating deviceis not used under high temperature, there is no need to necessarily usethe heat-resistant plates 53 a and 53 b. In a case where theheat-resistant plates 53 a and 53 b are not used in this manner, thethickness of the non-conductive soft magnetic plate which is housed inthe depressed portion of the shielding plate may also be set to be thesame as the depth of the depressed portion. In this manner, thethickness of the non-conductive soft magnetic plate may also be the sameas the depth of the depressed portion and may also be less than thedepth of the depressed portion.

MODIFIED EXAMPLES

<Shielding Plate>

FIGS. 6A to 6C are diagrams showing modified examples of theconfiguration of the shielding plate. FIGS. 6A and 6B respectively showthe first and the second modified examples of the shielding plate andare diagrams showing the shielding plate when viewed from directly above(from the steel strip 10 side). These drawings correspond to FIG. 4A.

In FIG. 6A, a shielding plate 61 is made of copper and has depressedportions 62 a and 62 b (62) disposed to have a distance therebetween inthe conveyance direction of the steel strip 10 and having the same sizeand shape. In these points, the shielding plate 61 is the same as theshielding plate 31 shown in FIGS. 4A to 4C. However, as shown in FIG.6A, the shape (the opening shape) in the plate face direction of thedepressed portion 62 a is a triangle which is tapered off toward theupstream side from the downstream side in the conveyance direction (adirection of an arrow shown in FIGS. 6A and 6B) of the steel strip 10and in which the corner portions 64 a to 64 c (64) are rounded. In sucha case, it is preferable that at least the corner portion 64 a which isa “corner portion on the upstream side in the conveyance direction ofthe steel strip 10” of the depressed portion 62 a be rounded so as toprotrude in the upstream side direction.

Further, the shape (the opening shape) in the plate face direction ofthe depressed portion 62 b is a triangle which is tapered off toward thedownstream side from the upstream side in the conveyance direction ofthe steel strip 10 and in which the corner portions 64 d to 64 f (64)are rounded. In such a case, it is preferable that at least the cornerportion 64 d which is a “corner portion on the downstream side in theconveyance direction of the steel strip 10” of the depressed portion 62b be rounded so as to protrude in the downstream side direction.

Further, the non-conductive soft magnetic plates and the heat resistantplates 63 a and 63 b (63), each of which has a shape corresponding withthe shape (the shape of a cross-section perpendicular to the thicknessdirection of the shielding plate 61) in the plate face direction of thebottom portion of each of the depressed portions 62 a and 62 b, arehoused in the depressed portions 62 a and 62 b and fixed thereto usingan adhesive or the like.

Further, in FIG. 6B, a shielding plate 71 is made of copper. As shown inFIG. 6B, the number of depressed portions 72 which are formed in theshielding plate 71 is one. As shown in FIG. 6B, the shape in the plateface direction of the depressed portion 72 is a shape in which the“corner portion (the corner portion 54 b) on the upstream side in theconveyance direction of the steel strip 10” of the depressed portion 51a shown in FIGS. 4A to 4C and the “corner portion (the corner portion 54e) on the downstream side in the conveyance direction of the steel strip10” of the depressed portion 51 b are connected to each other, and thecorner portions 74 a to 74 f (74) are rounded. Further, a non-conductivesoft magnetic plate and a heat resistant plate 73, each of which has ashape corresponding with the shape (the shape of a cross-sectionperpendicular to the thickness direction of the shielding plate 71) inthe plate face direction of the bottom portion of the depressed portion72, are housed in the depressed portion 72 and fixed thereto using anadhesive or the like.

As described above, it is preferable that a portion (a second portion)which is tapered off toward the upstream side from the downstream sidein the conveyance direction of the steel strip 10 and a portion (a firstportion) which is tapered off toward the downstream side from theupstream side in the conveyance direction of the steel strip 10 beincluded in the depressed portion which is formed in the shieldingplate. The first portion and the second portion may also be formedindividually (FIGS. 4A and 6A) and may also be formed integrally (FIG.6B). In addition, it is preferable that the tapered first and secondportions face each other in the conveyance direction of the steel strip10. If the shape in the plate face direction of the depressed portion issuch a shape, it becomes possible to form the edge of the depressedportion of the shielding plate according to a pathway of an eddy currentflowing through the steel strip 10. Further, in this case, it ispreferable that at least the tapered end portion (the tapered portion)among the “corner portions on the upstream side and the downstream sidein the conveyance direction of the steel strip 10” of the depressedportion be rounded.

In addition, the shape (the opening shape) in the plate face directionof the depressed portion which is formed in the shielding plate may alsobe any shape and the number thereof may also be 1 and may also be 2 ormore.

Further, it is preferable that a portion (a third portion) which istapered off toward a side close to the central portion in the widthdirection (a direction perpendicular to the conveyance direction) of theconductive sheet from a side away from the central portion in the widthdirection of the conductive sheet be included in the depressed portion.In this case, it is possible to gradually increase the amount of changein the effect in which the magnetic field that is generated by the eddycurrent flowing in the shielding plate pushes the side end of the steelstrip into the center side in the width direction of the steel strip, sothat suppression of meandering of the conductive sheet can be moreflexibly controlled. For example, in FIG. 4A, two third portions areincluded in the two depressed portions 51 a and 51 b of the shieldingplate 31. In addition, only a single depressed portion may be formed inthe shielding plate and the third portion may be included in the singledepressed portion. However, if a plurality of third portions is includedin the depressed portion of the shielding plate, it is possible to moreuniformly produce the above-mentioned push-in effect. Further, a portion(a fourth portion) which is tapered off toward a side away from thecentral portion in the width direction of the conductive sheet from aside close to the central portion in the width direction of theconductive sheet may also be included.

FIG. 6C shows the third modified example of the shielding plate and is avertical cross-sectional views of the shielding plate when cut in thethickness direction of the shielding plate along the conveyancedirection of the steel strip 10. FIG. 6C corresponds to FIG. 4B.

In FIG. 6C, a shielding plate 81 is made of copper and has depressedportions 82 a and 82 b (82) disposed to have a distance therebetween inthe conveyance direction of the steel strip 10 and having the same sizeand shape. Further, the shape (the opening shape) in the plate facedirection of each of the depressed portions 82 a and 82 b is a rhombusin which each corner portion is rounded. In this manner, the shieldingplate 81 shown in FIG. 6C and the shielding plate 31 shown in FIGS. 4Ato 4C are the same in material, shape, and size. However, the shieldingplate 81 shown in FIG. 6C is formed by superimposing an upper plate 84 aand a lower plate 84 b on each other and fixing them to each other.

As described above, the shielding plate may also be integrally formedand may also be formed by combining a plurality of members.

Moreover, although in this embodiment, the shielding plate is made ofcopper, the shielding plate is not limited to a copper plate. That is,provided that the shielding plate is a conductor, preferably, aconductor having a relative permeability of 1, the shielding plate mayalso be formed of any material. For example, the shielding plate can beformed of aluminum.

In addition, in this embodiment, by increasing the magnitude of the eddycurrent in the shielding plate which is generated in the vicinity of thenon-conductive soft magnetic plate (the non-conductive soft magneticmaterial), the magnitude of the eddy current which flows in the side endportion of the steel strip (the conductive sheet) 10 due to the mainmagnetic flux is reduced. Further, since the conductive shielding plateis interposed between the core (or, the heating coil) and thenon-conductive soft magnetic plate, direct passage of the main magneticflux through the non-conductive soft magnetic plate can be avoided. Forthis reason, it is acceptable if the induction heating device includesthe heating coil, the core, the conductive shielding plate which isdisposed between the core and the side end portion in a directionperpendicular to the conveyance direction of the steel strip, and thenon-conductive soft magnetic plate which is attached to the shieldingplate such that the shielding plate is interposed between the core andthe non-conductive soft magnetic plate.

For this reason, for example, shielding plates in which thenon-conductive soft magnetic plates as shown in FIGS. 7A to 7C and 8A to8C are mounted can be used. In addition, FIGS. 7A to 7C are verticalcross-sectional views showing one example of the configuration of eachof shielding plates in the fourth to the sixth modified examples of thisembodiment. Further, FIGS. 8A to 8C are perspective views showing oneexample of the configuration of each of shielding plates in the seventhto the ninth modified examples of this embodiment.

In the fourth modified example of this embodiment shown in FIG. 7A,non-conductive soft magnetic plates 102 a and 102 b (102) are disposedon a flat shielding plate 101 and the non-conductive soft magneticplates 102 face the side end portion of the steel strip. In this manner,the non-conductive soft magnetic plates may also be mounted on theshielding plate such that protruded portions are formed on the shieldingplate, without forming a depressed portion in the shielding plate. Inthis case, it is possible to increase an eddy current in the shieldingplate in a peripheral portion of the contact surface between theshielding plate and the non-conductive soft magnetic plate. However,since by forming a depressed portion in a shielding plate and disposinga non-conductive soft magnetic plate in the depressed portion, an eddycurrent can be constrained in an edge of the depressed portion and thedistance between an edge of the depressed portion and the non-conductivesoft magnetic plate can be reduced, it is possible to secure a largereddy current at the edge of the depressed portion. For this reason, asshown in FIG. 7B (the fifth modified example), it is also acceptablethat depressed portions 114 a and 114 b (114) be formed in a shieldingplate 111 and non-conductive soft magnetic plates 112 a and 112 b (112)be mounted in the depressed portions 114 of the shielding plate 111 suchthat protruded portions are formed on the shielding plate 111. Further,as shown in FIG. 7C (the sixth modified example), non-conductive softmagnetic plates 122 a and 122 b (122) in which the shape of the uppersurface and the shape of the lower surface are different from each othermay also be mounted in depressed portions 124 a and 124 b (124) of ashielding plate 121.

Further, in the seventh modified example shown in FIG. 8A, anon-conductive soft magnetic plate 202 is mounted on a shielding plate201 having protruded portions (two rhombic portions) 205 a and 205 b(205). In this case, it is possible to increase eddy currents flowing inedges of the protruded portions 205. Further, the shape (the outerperipheral shape) of the shielding plate is not particularly limited. Inthe eighth modified example shown in FIG. 8B, depressed portions (tworhombic portions) 214 a and 214 b (214) are formed in a shielding plate211 and the shielding plate 211 has frame portions 216 a and 216 bfollowing the outer peripheral shapes (the opening shapes) of thedepressed portions 214. Further, non-conductive soft magnetic plates 212a and 212 b (212) are housed in the depressed portions 214. In thiscase, it is possible to increase eddy currents flowing in edges of thedepressed portions 214. Further, in the ninth modified example shown inFIG. 8C, protruded portions (two rhombic portions) 225 a and 225 b (225)are formed on a shielding plate 221 and the shielding plate 221 has anouter peripheral shape similar to (following) the outer peripheralshapes (the base end shapes) of the protruded portions 225. Further, anon-conductive soft magnetic plate 222 is disposed on the shieldingplate 221 so as to surround edge portions of the protruded portions 225.In this case, it is possible to increase eddy currents flowing in edgesof the protruded portions 225.

In addition, a heat-resistant plate may also be mounted on thenon-conductive soft magnetic plate in each modified example shown inFIGS. 7A to 7C and 8A to 8C. Further, the shape and the number ofdepressed portions or protruded portions of the shielding plate in theplate face direction are not particularly limited. Further, the shapeand the number of non-conductive soft magnetic plates are also notparticularly limited.

It is preferable to make the magnitude of the eddy current in theshielding plate which flows through the vicinity of the non-conductivesoft magnetic plate, as large as possible. In the following, theconfiguration of making the eddy current larger will be described.

FIG. 4E is a cross-sectional view as viewed from a direction of C-C′ inFIG. 4B. As shown in FIG. 4E, the non-conductive soft magnetic plates 52a and 52 b (52) are included in the cross section, and a boundaryportion (a boundary line) between the shielding plate 31 and each of thenon-conductive soft magnetic plates 52 describes a closed curve (a totalof two closed curves). That is, a case where the shielding platesurrounds the non-conductive soft magnetic plate and a case where thenon-conductive soft magnetic plate surrounds the shielding plate areincluded in the cross section. In this manner, if the shielding platehas a cross section perpendicular to the thickness direction includingthe non-conductive soft magnetic material (a cross section parallel tothe coil face), the distance between the non-conductive soft magneticplate and the eddy current in the shielding plate, which is strengthenedby the non-conductive soft magnetic plate, can be shortened. Further,the above-mentioned boundary portion describes a closed curve (isring-shaped), whereby an area of an eddy current which is strengthenedcan increase and the characteristic of the non-conductive soft magneticplate can be fully utilized. In addition, in order to make the magnitudeof the eddy current in the shielding plate which flows through thevicinity of the non-conductive soft magnetic material, as large aspossible, it is preferable that the shielding plate and thenon-conductive soft magnetic material be in contact with each other.However, a space (a space as a boundary portion) may also be presentbetween the shielding plate and the non-conductive soft magneticmaterial such that the non-conductive soft magnetic material can beeasily attached to the shielding plate.

Further, in the case of using the induction heating device under hightemperature or the case of rapidly heating the steel strip, thetemperature of the shielding plate sometimes becomes high due to an eddycurrent. In this case, it is preferable to cool the shielding plate andthe non-conductive soft magnetic material using a cooler such as awater-cooling pipe. This cooling method is not particularly limited. Forexample, the shielding plate may also be cooled by integrally forming awater-cooling line in the shielding plate, or the shielding plate mayalso be cooled by sending a gas to the shielding plate by a blower.

<Non-Conductive Soft Magnetic Plate and Heat-Resistant Plate>

A material constituting the non-conductive soft magnetic plate is notlimited to a soft magnetic ferrite, provided that it is a non-conductivesoft magnetic material. Further, the non-conductive soft magneticmaterial may also be a material in which powder or particles are packedor compacted, or a material in which a plurality of blocks is combined,rather than a plate. Further, the shape of the non-conductive softmagnetic plate is not particularly limited. If it is possible to disposea non-conductive soft magnetic plate according to the portion (forexample, the edge of the depressed portion) of the inside of theshielding plate, in which the eddy current flows, since it is possibleto obtain a magnetic field which enhances the eddy current, for example,the non-conductive soft magnetic plate may also have a hollow portion.However, in order to sufficiently use the magnetism of thenon-conductive soft magnetic plate, it is preferable that thenon-conductive soft magnetic plate be solid.

The heat-resistant plate also need not necessarily be a plate and mayalso be any material, provided that a heat-resistant material is used.

Further, a method of fixing the non-conductive soft magnetic plate andthe heat-resistant plate which are housed in the depressed portion, tothe inside of the depressed portion is not limited to a method using anadhesive. For example, it is possible to fix them to the depressedportion using a screw with insulation secured between the shieldingplate and the non-conductive soft magnetic plate and the heat-resistantplate.

<Others>

In this embodiment, the disposition place of the induction heatingdevice 20 is not limited to the position shown in FIG. 1. That is,provided that it is possible to inductively heat a conductive sheet by atransverse method, the induction heating device 20 may also be disposedanywhere. For example, the induction heating device 20 may also bedisposed in the second container 12. Further, the induction heatingdevice 20 may also be applied to places other than the continuousannealing line.

Further, in this embodiment, a case where the heating coil width and thegap between the heating coils are equal to each other has been describedas an example. However, the heating coil width and the size of the gapare not particularly limited. However, it is preferable that the heatingcoil width be equal to or greater than the gap (or, the heating coilwidth be greater than the gap). In this case, a main magnetic fieldwhich is generated from the induction heating device 20 becomes morethan a leak magnetic field, thereby being able to improve the heatingefficiency of the induction heating device 20. In addition, the upperlimit of the heating coil width can be appropriately determinedaccording to the conditions such as a space where the induction heatingdevice 20 is disposed, or the weight or the cost which is required forthe induction heating device 20. Further, the numbers of heating coilsand cores disposed are not particularly limited. For example, aplurality of the heating coil and the core can be disposed in theconveyance direction of the steel strip in order to flexibly perform theheating control of the steel strip.

In addition, the number of shielding plates disposed is also notparticularly limited. For example, a plurality of the shielding platesmay also be disposed in the conveyance direction of the steel strip inaccordance with the numbers of heating coils and cores disposed. Aplurality of shielding plates having a single depressed portion may alsobe disposed to form a shielding plate unit having a plurality ofdepressed portions.

Further, in this embodiment, a case where the upper side inductor 21 andthe lower side inductor 22 are provided has been shown as an example.However, only one of either the upper side inductor 21 or the lower sideinductor 22 may also be provided.

In addition, all the embodiments of the present invention describedabove merely show examples embodied in implementation of the presentinvention and the technical scope of the present invention should not beconstrued as being limited by these. That is, the present invention canbe implemented in various forms without departing from the technicalidea thereof or the main features thereof.

INDUSTRIAL APPLICABILITY

A transverse flux induction heating device is provided which allowsunevenness of a temperature distribution in the width direction of aconductive sheet of a heating target to be reduced and allows variationin temperature distribution in the width direction of the conductivesheet of the heating target due to meandering of the conductive sheet tobe reduced.

REFERENCE SYMBOL LIST

-   -   10: steel strip (conductive sheet)    -   18: alternating-current power supply unit    -   20: induction heating device    -   21: upper side inductor    -   22: lower side inductor    -   23, 27: core    -   24: upper side heating coil (heating coil)    -   28: lower side heating coil (heating coil)    -   31, 61, 71, 81, 101, 111, 121, 201, 211, 221: shielding plate    -   51, 62, 72, 82, 114, 124, 214: depressed portion    -   205, 225: protruded portion    -   52, 102, 112, 122, 202, 212, 222: non-conductive soft magnetic        plate (non-conductive soft magnetic material)    -   53, 63, 73: heat-resistant plate (heat-resistant material)

The invention claimed is:
 1. A transverse flux induction heating device which inductively heats a conductive sheet by allowing an alternating magnetic field to intersect a sheet face of the conductive sheet, the conductive sheet being conveyed in one direction, the transverse flux induction heating device comprising: a heating coil disposed such that a coil face faces the sheet face of the conductive sheet; a core around which the heating coil is coiled; a shielding plate formed of a conductor and disposed between the core and a side end portion of the conductive sheet in a direction perpendicular to a conveyance direction of the conductive sheet, the shielding plate facing the side end portion; and a non-conductive soft magnetic material which is attached to the shielding plate, wherein the shielding plate is interposed between the core and the non-conductive soft magnetic material, a depressed portion formed in a surface of the shielding plate, the depressed portion having a depth (Dm), which is less than a thickness (D) of the shielding plate and which faces the side end portion in the direction perpendicular to the conveyance direction of the conductive sheet, the surface of the shielding plate facing the conductive sheet, the non-conductive soft magnetic material is housed in the depressed portion, the depressed portion including a first portion which is tapered off toward a downstream side from an upstream side in the conveyance direction of the conductive sheet and a second portion which is tapered off toward the upstream side from the downstream side in the conveyance direction of the conductive sheet are included in the depressed portion, and the first portion and the second portion face each other in the conveyance direction of the conductive sheet.
 2. The transverse flux induction heating device according to claim 1, further comprising: a heat-resistant plate which is attached to the non-conductive soft magnetic material and is positioned between the non-conductive soft magnetic material and the conductive sheet.
 3. The transverse flux induction heating device according to claim 1, wherein the shielding plate has a cross section parallel to the coil face, the cross section including the non-conductive soft magnetic material.
 4. The transverse flux induction heating device according to claim 1, wherein the depressed portion is formed in the surface of the shielding plate to be tapered off toward a side end portion of the shielding plate in a width direction of the shielding plate from a central portion of the shielding plate in the width direction of the shielding plate.
 5. The transverse flux induction heating device according to claim 1, wherein the first portion is rounded toward the downstream side, and the second portion is rounded toward the upstream side. 